Electrode of lithium ion battery and lithium ion battery using the same

ABSTRACT

An electrode of a lithium ion battery includes a current collector, an electrode material layer disposed on a top surface of the current collector, and a protective film located on a top surface of the electrode material layer. A composition of the protective film is at least one of Al x M y PO 4  and Al x M y (PO 3 ) 3 , M represents at least one chemical element of Cr, Zn, Mg, Zr, Mo, V, Nb, and Ta, and a valence of M is represented by k, wherein 0&lt;x&lt;1, 0&lt;y&lt;1, and 3x+ky=3.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division application of U.S. patent applicationSer. No. 13/034924, filed on Feb. 25, 2011, entitled “ELECTRODE OFLITHIUM ION BATTERY, METHOD FOR MAKING THE SAME, AND LITHIUM ION BATTERYUSING THE SAME”, which claims all benefits accruing under 35 U.S.C. §119from China Patent Applications No. 201010264760.5, filed on Aug. 27,2010, No. 201010264757.3, filed on Aug. 27, 2010, No. 201010555227.4,filed on Nov. 23, 2010, and No. 201010555228.9, filed on Nov. 23, 2010,in the China Intellectual Property Office, the contents of which arehereby incorporated by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to an electrode having a protective filmand a lithium ion battery including the electrode.

2. Description of Related Art

Lithium ion batteries mainly include a cathode, an anode, a separator,and an electrolyte. The performance of electrode active materials of thecathode and anode is a key factor, which influences the performance ofthe lithium ion battery.

Cathode active materials can be LiCoO₂, LiNiO₂, LiMn₂O₄, and LiFePO₄.Anode active materials can be carbonaceous materials such as graphiteand carbon nanotubes. A method for making an electrode includes stepsof: mixing the electrode active materials, a conductive agent, and abinder as slurry; coating the slurry on a surface of a currentcollector, and heating the coated current collector to achieve theelectrode. However, unwanted chemical reactions may occur duringcharging and discharging of the lithium ion battery, especially at ahigh temperature. For example, some substance of the electrolyte maycorrode the electrode active material or current collector such asaluminum foil. The separator may have an unacceptable shrinkage or mayfuse at high temperatures. Thus, the lithium battery may have a lowstability, and a capacity lost during the cycling process, especially atthe high temperatures.

AlO₄ has been studied as a material to improve the thermal stability ofthe lithium ion battery (referring to the article “Correlation betweenAlPO₄ nanoparticle coating thickness on LiCoO₂ cathode and thermalstability. J. Cho, Electrochimica Acta 48 (2003) 2807-2811”).

In this article, a dispersion of AlPO₄ particles dispersed in the wateris prepared first, and then LiCoO₂ cathode particles are added into thedispersion. Referring to FIG. 10, the AlPO₄ particles 602 are adhered tothe surface of the LiCoO₂ cathode particles 604. After drying and heattreating processes, the LiCoO₂ cathode particles 604 are coated with theAlPO₄ particles 602. However, the small AlPO₄ particles 602 agglomerateeasily with each other in water because it is water insoluble.

When many LiCoO₂ cathode particles 604 are added in the dispersion, thefirst added LiCoO₂ cathode particles 604 adhere to many AlPO₄ particles602, and subsequently added LiCoO₂ cathode particles 604 may not adhereto enough AlPO₄ particles 602. Even though the LiCoO₂ cathode particles604 are wholly coated, the AlPO₄ particles 602 having uneven sizes aredistributed on the surface of the cathode active material 604. Thus, thecoated layer of AlPO₄ particles 602 is non-uniform. Therefore, cyclingperformance of the lithium ion battery including this product 600 is notmaximized. Further, it is difficult to use the AlPO₄ particle dispersionto improve other parts of the lithium battery, such as the separator andthe current collector.

What is needed, therefore, is to provide an electrode of the lithium ionbattery which when applied to the lithium ion battery can increase itsstability and safety.

BRIEF DESCRIPTION OF THE DRAWING

Many aspects of the present disclosure can be better understood withreference to the following drawings. The components in the drawings arenot necessarily to scale, the emphasis instead being placed upon clearlyillustrating the principles of the present embodiments.

FIG. 1 is a flowchart of an embodiment of a method for making a modifierfor a lithium ion battery.

FIG. 2 is a schematic side view of an embodiment of a current collectorof a lithium ion battery fabricated using the modifier.

FIG. 3 shows a scanning electron microscope (SEM) image of the currentcollector of the lithium ion battery.

FIG. 4 shows a SEM image of a conventional current collector of thelithium ion battery.

FIG. 5 is a schematic side view of an embodiment of an electrode of thelithium ion battery fabricated using the modifier.

FIG. 6 is a schematic view of an embodiment of an electrode compositematerial of the lithium ion battery fabricated using the modifier.

FIG. 7 is a schematic side view of an embodiment of a separator of thelithium ion battery fabricated using the modifier.

FIG. 8 is a comparison plot showing a testing result of the heatshrinkage of the separator compared with a comparing separator oflithium ion battery.

FIG. 9 is a partial section view of an embodiment of a lithium ionbattery.

FIG. 10 is a schematic view of a conventional cathode active materialcoated with aluminum phosphate.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “another,” “an,” or “one” embodiment in this disclosure are notnecessarily to the same embodiment, and such references mean at leastone.

An embodiment of an electrode of lithium ion battery of the presentdisclosure is fabricated using a modifier of the lithium ion battery, sothe modifier is introduced first in present disclosure.

Modifier of Lithium Ion Battery and Method for Making the Same

One embodiment of a modifier of a lithium ion battery includes a mixtureof a phosphorus source having a phosphate radical, a trivalent aluminumsource, and a metallic oxide in a liquid phase solvent.

The phosphate radical can be orthophosphoric radical (PO₄ ³⁻),dihydrogen phosphate radical (H₂PO₄ ⁻), hydrophosphate radical (HPO₄²⁻), or any combination thereof. The phosphorus source having anorthophosphoric radical can be at least one of phosphoric acid (H₃PO₄),triammonium phosphate ((NH₄)₃PO₄), and aluminum phosphate (AlPO₄). Thephosphorus source having a dihydrogen phosphate radical can be at leastone of ammonium dihydrogen phosphate (NH₄H₂PO₄) and aluminum dihydrogenphosphate (Al(H₂PO₄)₃). The phosphorus source having a hydrophosphateradical can be at least one of diammonium hydrogen phosphate((NH₄)₂HPO₄) and dialuminum hydrogen phosphate (Al₂(HPO₄)₃). Thetrivalent aluminum source can be at least one of aluminumhydroxide(Al(OH)₃), aluminum oxide (Al₂O₃), aluminum phosphate (AlPO₄),aluminum dihydrogen phosphate (Al(H₂PO₄)₃), and dialuminum hydrogenphosphate (Al₂(HPO₄)₃). The phosphorus source having a phosphate radicaland the trivalent aluminum source both can be AlPO₄, Al(H₂PO₄)₃,Al₂(HPO₄)₃, or any combination thereof. The metallic oxide can be atleast one of chromium trioxide (CrO₃), zinc oxide (ZnO), copper oxide(CuO), magnesium oxide (MgO), zirconium dioxide (ZrO₂), molybdenumtrioxide (MoO₃), vanadium pentoxide (V₂O₅), niobium pentoxide (Nb₂O₅),and tantalum pentoxide (Ta₂O₅).

The modifier is a clear solution having some stickiness. The liquidphase solvent of the modifier can be water or N-methyl-pyrrolidone(NMP). In one embodiment, a molar ratio of the trivalent aluminumsource, the metallic oxide, and the phosphorus source is set by(Mol_(Al)+Mol_(Metal)):Mol_(p)=about 1:2.5 to about 1:4, whereinMol_(Al) is the amount of substance of the aluminum element in thetrivalent aluminum source, Mol_(Metal) is i the amount of substance ofthe metallic element in the metallic oxide, and Mol_(p) is the amount ofsubstance of the phosphorus element in the phosphorus source. In oneembodiment, the (Mol_(Al)+Mol_(Metal)):Mol_(p) is in a range from about1:2.5 to about 1:3. The modifier is a red clear solution if the metallicoxide is CrO₃. A concentration of the modifier can be adjusted accordingto an actual need for the thickness of a coating layer formed by themodifier. The liquid phase solvent can dilute the modifier to a lowconcentration to form a relatively thin coating layer. The concentrationof the modifier can be represented by a total mass of the phosphateradical, the aluminum element and the metallic element divided by avolume of the modifier (i.e., a mass of the phosphate radical+a mass ofthe aluminum element+a mass of the metallic element/a volume of themodifier). In one embodiment, the concentration is in a range from about0.02 grams per milliliter (g/ml) to about 0.08 g/ml. The modifier can becoated on the surface of a current collector or an electrode plate ofthe lithium ion battery. A reaction occurs when the modifier is heatedat a temperature higher than 100° C. The composition of the reactionproduct is at least one of Al_(x)M_(y)PO₄ and Al_(x)M_(y)(PO₃)₃. Mrepresents at least one chemical element of Cr, Zn, Mg, Zr, Mo, V, Nb,and Ta. A valence of M is represented by k, wherein 0<x<1, 0<y<1, and3x+ky=3. In one embodiment, M is Cr, k=3, and the composition of thereaction product is at least one of Al_(x)Cr_(1−x)PO₄ andA_(x)Cr_(1−x)(PO₃)₃.

Referring to FIG. 1, one embodiment of a method for making the modifierof lithium ion battery includes the following steps:

-   S1, providing the phosphorus source having the phosphate radical,    the trivalent aluminum source and the metallic oxide; and-   S2, mixing the phosphorus source having the phosphate radical, the    trivalent aluminum source, and the metallic oxide in the liquid    phase solvent to form a clear solution.

The liquid phase solvent can be water or N-methyl-pyrrolidone (NMP). Inone embodiment, a molar ratio of the trivalent aluminum source, themetallic oxide and the phosphorus source is set by(Mol_(Al)+Mol_(Metal)):Mol_(p)=about 1:2.5 to about 1:4, whereinMol_(Al) is the amount of substance of the aluminum element in thetrivalent aluminum source, Mol_(Metal) is the amount of substance of themetallic element in the metallic oxide, and Mol_(p) is the amount ofsubstance of the phosphorus element in the phosphorus source. In oneembodiment, the (Mol_(Al)+Mol_(Metal)):Mol_(p) is in a range from about1:2.5 to about 1:3.

The phosphorus source, the trivalent aluminum source and the metallicoxide can be added in the liquid phase solvent simultaneously or one byone. In one embodiment, the phosphorus source solution can be preparedfirst, and then the trivalent aluminum source and the metallic oxide canbe added into the phosphorus source solution, simultaneously or one byone. The adding order of the trivalent aluminum source and the metallicoxide does not influence the final reaction product. In one embodiment,the phosphorus source is H₃PO₄, the trivalent aluminum source isAl(OH)₃, and the metallic oxide is CrO₃. A concentration of the H₃PO₄ isin a range from about 60% to about 90%. The H₃PO₄ aqueous solution isprepared first, then the Al(OH)₃ powders are added into the aqueoussolution to react with the H₃PO₄. A white suspension of AlPO₄ is formedafter a period of time. The CrO₃ powders are then added into the whitesuspension. After a while, the white suspension disappears, and a redclear solution is produced.

The step S2 can further include a step of stirring and heating a mixtureof the phosphorus source, the trivalent aluminum source, and themetallic oxide in the liquid phase solvent to evenly mix the mixture andreact thoroughly. In one embodiment, the heating temperature is in arange from about 60° C. to about 100° C. A time period for the stirringand heating can be in a range from about 2 hours to about 3 hours.

The following example further illustrates the modifier and the methodfor making the modifier.

Example 1 Preparation of the Modifier

About 34.5 g of H₃PO₄ having a concentration of about 85% and about 14 gof deionized water are mixed as a solution in a container. The solutionis magnetically stirred at about 80° C. for about 5 minutes. About 5.9 gof Al(OH)₃ powders are then added in the solution to react with theH₃PO₄ for about 2 hours. A colloidal suspension is formed in thecontainer. Further, about 2.5 g of CrO₃ powders are added in thecolloidal suspension to react for about 2 hours, to achieve a red clearsolution. The red clear solution is the modifier of the example 1.

Applications of the Modifier of Lithium Ion Battery

-   (a) Applying the Modifier to Current Collectors of Lithium Ion    Battery

The modifier can be applied to the current collector of the lithium ionbattery to increase the stability of the lithium ion battery. Themodifier can be easily coated on the surface of the current collector ofthe lithium ion battery such that an even and thin protective film canbe formed on the surface of the current collector after a heat treatingprocess. The protective film can prevent unwanted side reactions betweenthe current collector and the solvent of the electrolyte of the lithiumion battery. The protective film is thin and barely influences theconductivity of the current collector.

Referring to FIG. 2, one embodiment of a modified current collector 100of the lithium ion battery is prepared by using the modifier mentionedabove. The modified current collector 100 includes a metal plate 102 anda protective film 106 disposed on a surface of the metal plate 102. Thecomposition of the protective film 106 is at least one of Al_(x)M_(y)PO₄and Al_(x)M_(y)(PO₃)₃. M represents at least one chemical element of Cr,Zn, Mg, Zr, Mo, V, Nb, and Ta. A valence of M is represented by k,wherein 0<x<1, 0<y<1, and 3x+ky=3.

The material of the metal plate 102 can be metals such as aluminum (Al),copper (Cu), nickel (Ni), or alloys thereof, used as a conventionalcurrent collector in the lithium ion battery. In one embodiment, themetal plate 102 is an aluminum foil. In one embodiment, a thickness ofthe metal plate 102 is in a range from about 5 micrometers to about 60micrometers, and a width of the metal plate 102 is in a range from about10 millimeters to about 300 millimeters. A thickness of the protectivefilm 106 can be in a range from about 10 nanometers to about 200nanometers. In one embodiment, the thickness of the protective film 106is in a range from about 50 nanometers to about 60 nanometers. In oneembodiment, the composition of the protective film 102 is at least oneof Al_(x)Cr_(1−x)PO₄ and Al_(x)Cr_(1−x)(PO₃)₃.

One embodiment of a method for making the modified current collector 100of the lithium ion battery using the modifier includes the followingsteps:

-   S21, providing the modifier prepared by the method mentioned above    and the metal plate 102;-   S22, coating the modifier on the surface of the metal plate 102 to    form a coating layer; and-   S23, heat treating the coated metal plate 102 to transform the    coating layer into a protective film 106 formed on the surface of    the metal plate 102.

In step S22, the modifier can be evenly coated on one or two surfaces ofthe metal plate 102 by methods such as knife coating, brushing,spraying, electrostatic coating, roll coating, screen printing, or dipcoating. A thick coating layer may be unacceptable, because theconductivity of the metal plate 102 decreases with a thick coatinglayer. Dip coating can form an even and continuous coating layer onopposite surfaces of the metal plate 102 simultaneously, and using thedip coating method can conveniently control the thickness of the coatinglayer. In one embodiment, dip coating is used to coat the modifier onthe two surfaces of the metal plate 102.

Dip coating includes the steps of completely dipping the metal plate 102into the prepared modifier, and then lifting the coated metal plate 102out from the modifier. The metal plate 102 can be substantiallyperpendicular to the level of the modifier during the lifting process.The steps of dipping and lifting can be repeated several times tocontrol the thickness and uniformity of the coating layer on the surfaceof the metal plate 102. A thinner coating layer can be formed byreducing the concentration of the modifier and dipping and lifting thedipped metal plate 102 in and out of the modifier at a faster rate.

The coated metal plate 102 can be dried to remove the liquid phasesolvent of the coating layer before the heat treating process of thestep S23. The coated metal plate 102 can be air dried or heat dried.

In step S23, the heat treating step not only can further evaporate theliquid phase solvent of the coating layer, but also transform thecoating layer into a continuous protective film 106 formed on thesurface of the metal plate 102. The protective film 106 can prevent themetal plate 102 from corroding the substance in the electrolyte of thelithium ion battery. A temperature of the heat treating process can bein a range from about 100° C. to about 350° C. In one embodiment, thetemperature of the heat treating process is in a range from about 150°C. to about 250° C. A time period for the heat treating process can bein a range from about 1 hour to about 3 hours.

As a sticky clear solution, the modifier can be easily coated on thesurface of the metal plate 102 of the modified current collector 100,and an even and thin protective film 106 can be formed on the surface ofthe metal plate 102 of the modified current collector 100 after the heattreating process. The protective film 106 can prevent unwanted sidereactions of the modified current collector 100 and the substance in theelectrolyte of the lithium ion battery. The protective film 106 barelyinfluences the conductivity of the modified current collector 100.

The following example further illustrates the modified current collector100 of the present disclosure.

Example 2 Preparation of the Modified Current Collector 100 of theLithium Ion Battery

An aluminum foil with 20 microns thickness and 30 millimeters width isused as the metal plate 102. About 0.5 ml Triton and about 30 ml ofwater are added to the prepared modifier in the Example 1 to dilute themodifier. The Triton and water added causes the aluminum foil to immerseeasily with the modifier. The diluted modifier is ultrasonicallyvibrated. The diluted modifier is coated on the surface of the aluminumfoil by using the dip-coating method. The coated aluminum foil is driedin an oven at about 80° C. for about half of an hour, and then heattreated in the muffle furnace at about 200° C. for about an hour,thereby forming the protective layer 106 on the modified currentcollector 100. The thickness of the protective film 106 is about 52nanometers.

The concentration of the diluted modifier is about 0.0432 g/ml.

A conventional aluminum current collector is used to compare with themodified current collector 100 prepared in the Example 2. First, themodified current collector 100 and the conventional aluminum currentcollector are observed in the SEM to compare their surface morphology.Referring to FIG. 4, there are many defect holes in the surface of theconventional aluminum current collector. Referring to FIG. 3, thesurface of the modified current collector 100 having the protective film106 prepared in the Example 2 is smooth and dense.

The corrosion resistance of the modified current collector 100 of theExample 2 and the conventional aluminum current collector that have beenobserved in the SEM is also compared. The modified current collector 100of the Example 2 is immersed in a container with hydrochloric acid, andthe conventional aluminum current collector is immersed in anothercontainer with hydrochloric acid. Bubbles are observed on the surface ofthe conventional aluminum current collector after a period of time,indicating that the conventional aluminum current collector has beeneroding. There are no bubbles observed on the surface of the modifiedcurrent collector 100 of the Example 2 immersed in the hydrochloric acidfor 4 hours. The conductivity of the modified current collector 100 ofthe Example 2 is also tested. The result indicates that the modifiedcurrent collector 100 having the protective film 106 still has goodconductivity, and can meet the requirements when it is used in thelithium ion battery.

(b) Applying the Modifier to Electrode Material Layers of the LithiumIon Battery

Referring to FIG. 5, one embodiment of an electrode 200 of the lithiumion battery includes a current collector 202, an electrode materiallayer 204 disposed on a top surface of the current collector 202, and aprotective film 206 located on a top surface of the electrode materiallayer 204. The composition of the protective film 206 is at least one ofAl_(x)M_(y)PO₄ and Al_(x)M_(y)(PO₃)₃. M represents at least one ofchemical elements of Cr, Zn, Mg, Zr, Mo, V, Nb, and Ta. A valence of Mis represented by k, wherein 0<x<1, 0<y<1, and 3x+ky=3. The protectivefilm 206 is fabricated using the modifier of the lithium ion batterymentioned above. In one embodiment, the composition of the protectivefilm 206 can be at least one of Al_(x)Cr_(1−x)PO₄ andAl_(x)Cr_(1−x)(PO₃)₃.

The material of the current collector 202 can be metals such as Al, Cu,Ni, or alloys thereof. The material of the electrode material layer 204includes an electrode active material, a conductive agent, and a binder.The electrode active material can be a cathode active material for acathode electrode or an anode active material for an anode electrode.The cathode active material can be doped or undoped spinel lithiummanganese oxide, layered lithium manganese oxide, lithium nickel oxide,lithium cobalt oxide, lithium iron phosphate, lithium nickel manganeseoxide, lithium nickel cobalt oxide, or any combination thereof.Specifically, the formula of the spinel lithium manganese oxide can beLi_(x)Mn_(2−y)L_(y)O₄. The formula of the lithium nickel oxide can beLi_(x)Ni_(1−y)L_(y)O₂. The formula of the lithium cobalt oxide can beLi_(x)Co_(1−y)L_(y)O₂. The formula of the layered lithium manganeseoxide can be Li_(x)Mm_(1−y)L_(y)O₂. The formula of the lithium ironphosphate can be Li_(x)Fe_(1−y)L_(y)PO₄. The formula of the lithiumnickel manganese oxide can beLi_(x)Ni_(0.30 z−a)Mn_(1.5−z−b)L_(a)R_(b)O₄. The formula of the lithiumnickel cobalt oxide can be Li_(x)Ni_(c)Co_(d)Mn_(e)L_(f)O₂. In the aboveformulas, 0.1≦x≦1.1, 0≦y<1, 0≦z<1.5, 0≦a-z<0.5, 0≦b+z<1.5, 0<c<1, 0<d<1,0<e<1, 0≦f≦0.2, and c+d+e+f=1. L and R represent at least one of thechemical elements of alkali metal elements, alkaline-earth metalelements, Group-13 elements, Group-14 elements, transition metalelements, and rare-earth elements. In one embodiment, L and R representat least one of the chemical elements of Mn, Ni, Cr, Co, V, Ti, Al, Fe,Ga, Nd, and Mg. The anode active material can be lithium titanate,graphite, acetylene black, organic cracking carbon, mesocarbonmicrobeads (MCMB), or any combination thereof. More specifically, theformula of the lithium titanate can be Li_((4−g))A_(g)Ti₅O₁₂ orLi₄A_(h)Ti_((5−h))O₁₂, wherein 0<g<0.33 and 0<h<0.5. In the formula, ‘A’represents at least one of the chemical elements of alkali metalelements, alkaline-earth metal elements, Group-13 elements, Group-14elements, transition metal elements, and rare-earth elements. In oneembodiment, ‘A’ represents at least one of the chemical elements of Mn,Ni, Cr, Co, V, Ti, Al, Fe, Ga, Nd, and Mg. The conductive agent can beat least one of graphite, Polyvinylidene Fluoride (PVDF),Polytetrafluoroethylene (PTFE), and Styrene-Butadiene Rubber (SBR). Theelectrode active material, the conductive agent, and the binder can beother commonly used materials.

One embodiment of a method for making the electrode 200 by using themodifier includes the following steps:

-   S31, forming the electrode material layer 204 on the top surface of    the current collector 202;-   S32, coating the modifier on the top surface of the electrode    material layer 204 to form a coating layer; and-   S33, heat treating the coated current collector 202, wherein the    coating layer is transformed to a protective film 206 formed on the    top surface of the electrode material layer 204.

The step S31 further includes the steps of mixing the electrode activematerial particles, the conductive agent, and the binder to form aslurry and coating the slurry on the top surface of the currentcollector 202 to form the electrode material layer 204. The electrodematerial layer 204 can be adhered to the top surface of the currentcollector 202 by a heating process.

Because the clear solution is sticky, the modifier can be easily andevenly coated on the electrode material layer 204 by methods such asknife coating, brushing, spraying, electrostatic coating, roll coating,screen printing, or dip coating. A thick coating layer may decrease theconductivity of the electrode 200.

In step S33, the heat treating step not only can evaporate the liquidphase solvent of the coating layer, but also transform the coating layerinto a continuous protective film 206 formed on the surface of theelectrode material layer 204. The protective film 206 can prevent theelectrode active material in the electrode material layer 204 from thecorrosion of the substance in the electrolyte of the lithium ionbattery. The heat treating process temperature can be in a range fromabout 100° C. to about 200° C. A time period for the heat treatingprocess can be in a range from about 1 hour to about 3 hours. Athickness of the protective film 206 can be in a range from about 10nanometers to about 200 nanometers. In one embodiment, the thickness ofthe protective film 206 can be in a range from about 50 nanometers toabout 60 nanometers. The thin protective film 206 barely influences theconductivity of the electrode 200 of the lithium ion battery.

(c) Applying the Modifier to Individual Electrode Active MaterialParticle of the Lithium Ion Battery

The modifier of the lithium ion battery can be applied to increase thethermal stability and safety of the electrode active material. Referringto FIG. 6, one embodiment of an electrode composite material 300includes a plurality of electrode active material particles 302 and aprotective film 306 coated on the surface of each of the individualparticle 302. A composition of the protective film 306 is at least oneof Al_(x)M_(y)PO₄ and Al_(x)M_(y)(PO₃)₃. M represents at least one ofthe chemical elements of Cr, Zn, Mg, Zr, Mo, V, Nb, and Ta. A valence ofM is represented by k, wherein 0<x<1, 0<y<1, and 3x+ky=3. The stepsinclude coating the modifier on the surface of the electrode activematerial particle 302, and heat treating the coated electrode activematerial particle 302 to form the protective film 306 coated on thesurface of the electrode active material particle 302.

The protective film 306 can be coated evenly and continuously on thesurface of the electrode active material particle 302. In oneembodiment, a mass ratio of the protective film 306 to the electrodecomposite material 300 is in a range from about 0.05% to about 3%. Thethickness of the protective film 306 is in a range from about 5nanometers to about 100 nanometers. The material of the electrode activematerial particle 302 can be a cathode active material for a cathodeelectrode or an anode active material for an anode electrode. Thecathode active material can be doped or undoped spinel lithium manganeseoxide, layered lithium manganese oxide, lithium nickel oxide, lithiumcobalt oxide, lithium iron phosphate, lithium nickel manganese oxide,lithium nickel cobalt oxide, or any combination thereof. Specifically,the formula of the spinel lithium manganese oxide can beLi_(x)Mn_(2−y)L_(y)O₄. The formula of the lithium nickel oxide can beLi_(x)Ni_(1−y)L_(y)O₂. The formula of the lithium cobalt oxide can beLi_(x)Co_(1−y)L_(y)O₂. The formula of the layered lithium manganeseoxide can be Li_(x)Mn_(1−y)L_(y)O₂. The formula of the lithium ironphosphate can be Li_(x)Fe_(1−y)L_(y)PO₄. The formula of the lithiumnickel manganese oxide can beLi_(x)Ni_(0.5+z−a)Mn_(1.5−z−b)L_(a)R_(b)O₄. The formula of the lithiumnickel cobalt oxide can be Li_(x)Ni_(c)Co_(d)Mn_(e)L_(f)O₂. In the aboveformulas, 0.1≦x≦1.1, 0≦y<1, 0≦z<1.5, 0≦a-z<0.5, 0≦b+z<1.5, 0<c<1, 0<d<1,0<e<1, 0≦f≦0.2, and c+d+e+f=1. L and R represent at least one of thechemical elements of alkali metal elements, alkaline-earth metalelements, Group-13 elements, Group-14 elements, transition metalelements, and rare-earth elements. In one embodiment, L and R representat least one of the chemical elements of Mn, Ni, Cr, Co, V, Ti, Al, Fe,Ga, Nd, and Mg. The anode active material can be lithium titanate,graphite, acetylene black, organic cracking carbon, mesocarbonmicrobeads (MCMB), or any combination thereof. More specifically, theformula of the lithium titanate can be Li_((4−g))A_(g)Ti₅O₁₂ orLi₄A_(h)Ti_((5−h))O₁₂, wherein 0<g≦0.33 and 0<h≦0.5. ‘A’ represents atleast one of the chemical elements of alkali metal elements,alkaline-earth metal elements, Group-13 elements, Group-14 elements,transition metal elements, and rare-earth elements. In one embodiment,‘A’ represents at least one of the chemical elements of Mn, Ni, Cr, Co,V, Ti, Al, Fe, Ga, Nd, and Mg. In one embodiment, a diameter of theelectrode active material particle 302 is in a range from about 100nanometers to about 100 microns. The material of the electrode activematerial particle 302 can be other commonly used materials. In oneembodiment, graphite powder is used as the electrode active materialparticle 302 for the anode electrode. The diameter of the graphitepowder is in a range from about 8 microns to about 12 microns. Thecomposition of the protective film is at least one of Al_(x)Cr_(1−x)PO₄and Al_(x)Cr_(1−x)(PO₃)₃.

One embodiment of a method for making the electrode composite material300 of the lithium ion battery by using the modifier includes thefollowing steps:

-   B11, providing the modifier and the electrode active material    particles 302;-   B12, mixing the active material particles 302 and the modifier to    form a mixture; and-   B13, drying and heat treating the mixture.

In step B12, the step of mixing is a solid-liquid mixing. The electrodeactive material particle 302 is insoluble in the modifier. The modifiercan be wholly and easily coated on the surface of the each electrodeactive material particle 302 to form a thin and even coating layer.

The method can further include a step of filtering the coated electrodeactive material particles 302 from the modifier after the step B12.

In step B13, a method of the drying can be air drying or heat drying toremove the liquid phase solvent of the mixture. A temperature of theheat drying process can be in a range from about 60° C. to about 100° C.In one embodiment, the heat drying is used to dry the mixture, and thetemperature of the heat drying process is about 80° C. The heat treatingstep can transform the coating layer into an even and continuousprotective film 306 well coated on the surface of the each electrodeactive material particle 302. A temperature of the heat treating processcan be in a range from about 300° C. to about 800° C. A time period forthe heat treating process can be in a range from about 1 hour to about 3hours. In one embodiment, the temperature of the heat treating processis about 700° C. The time period for the heat treating process is about3 hours. A mass ratio of the protective film 306 to the electrodecomposite material 300 can be in a range from about 0.05% to about 3%.The thickness of the protective film 306 can be in a range from about 5nanometers to about 100 nanometers.

The modifier can be easily and wholly coated on the surface of eachelectrode active material particle 302 to form an even and continuousprotective film 306. The protective film 306 can insulate the transferof electrons between the electrode active material particles 306 and theelectrolyte of the lithium ion battery as well as allow the lithium ionsto pass. Therefore, the protective film 306 can increase the thermalstability and capacity retention of the lithium ion battery, and notdecrease the electrochemical performance of the lithium ion battery.

(d) Applying the Modifier to Separators of the Lithium Ion Battery

Referring to FIG. 7, one embodiment of a separator 400 of the lithiumion battery, fabricated using the modifier prepared in the Example 1,includes a porous membrane 402 and a modifier layer 404 disposed on thesurface of the porous membrane 402. The steps include coating themodifier on the surface of the porous membrane 402 to form a coatinglayer, and drying the coating layer to form the modifier layer 404.

The porous membrane 402 can be commonly used separators of the lithiumion battery, such as a pure polymer separator, a ceramic separator, or apolymer based separator having ceramic materials therein. A thickness ofthe porous membrane 402 can be in a range from about 5 microns to about60 microns. A porosity of the porous membrane 402 can be in a range fromabout 20% to about 90%. A diameter of the porous membrane 402 can be ina range from about 0.01 microns to about 80 microns. In one embodiment,the thickness of the porous membrane 402 is in a range from about 15microns to about 40 microns, the porosity of the porous membrane 402 isin a range from about 40% to about 80%, and the diameter of the porousmembrane 402 is in a range from about 0.1 microns to about 10 microns.

Two surfaces of the porous membrane 402 are coated with the modifierlayers 404. A thickness of the modifier layer 404 can be in a range fromabout 10 nanometers to about 100 nanometers. In one embodiment, thethickness of the modifier layer 404 is in a range from about 10nanometers to about 40 nanometers.

In one embodiment of a method for preparing the separator 400 of thelithium ion battery by using the modifier includes the following steps:

-   B21, providing the modifier of the lithium ion battery and the    porous membrane 402;-   B22, coating the modifier on the surface of the porous membrane 402    to form a coating layer; and-   B23, drying the coated porous membrane 402 to form the modifier    layer 404 disposed on the surface of the porous membrane 402.

In step B21, the porous membrane 402 can be prepared by a method of meltstretching or thermally induced phase separation.

In step B22, the modifier can be evenly coated on one or two surfaces ofthe porous membrane 402 by methods such as knife coating, brushing,spraying, electrostatic coating, roll coating, screen printing, or dipcoating. Dip coating maximizes the control of the thickness and evennessof the coating layer. In one embodiment, the dip coating method is usedto coat the modifier on opposite surfaces of the porous membrane 402.

More specifically, the dip coating method includes the steps ofcompletely dipping the porous membrane 402 into the prepared modifier,and lifting the dipped porous membrane 402 out from the modifier. Theporous membrane 402 can be substantially perpendicular to the level ofthe modifier during the lifting process. The steps of dipping andlifting can be repeated several times to control the thickness andevenness of the coating layer on the surface of the porous membrane 402.A thinner coating layer can be formed by reducing the concentration ofthe modifier and dipping and lifting the dipped porous membrane 402 inand out of the modifier at a faster rate.

In step B23, the liquid phase solvent of the modifier can be removed andthe formed modifier layer can be well combined with the surface of theporous membrane 402 by drying the coated porous membrane 402. The coatedporous membrane 402 can be dried by air drying or heat drying. Atemperature of the heat drying process may be equal to or lower than 70°C.

As a clear sticky solution, the modifier can be easily and evenly coatedon the surface of the porous membrane 404 to form a thin modifier layer404. The existence of the modifier layer 404 can increase the mechanicalstrength of the separator 400 and not decrease the lithium ion mobilitywhen applied to a lithium ion battery. The modifier layer 404 of theseparator 400 can be transformed to a continuous protective film toprevent the shrinkage of the separator 400 when its temperature reachesto or higher than 100° C. The thermal stability and the safety of thelithium ion battery thus can be increased. The composition of theprotective film can be at least one of Al_(x)M_(y)PO₄ andAl_(x)M_(y)(PO₃)₃. M represents at least one of the chemical elements ofCr, Zn, Mg, Zr, Mo, V, Nb, and Ta. A valence of M is represented by k,wherein 0<x<1, 0<y<1, and 3x+ky=3.

The following example further illustrates the separator 400 of thepresent disclosure.

Example 3 Preparation of the Separator 400 of the Lithium Ion Battery

A bare polypropylene porous membrane commonly used as a separator of thelithium ion battery with 60% porosity and 7 microns average diameter isused as the porous membrane 402 in the Example 3. The concentration ofthe modifier prepared in the Example 1 is diluted to about 1 mol/L. Thediluted modifier is then coated on opposite surfaces of thepolypropylene porous membrane using the dip coating method.

The coated polypropylene porous membrane is dried at about 40° C. forabout an hour. The separator 400 having the modifier layer 404 isformed. The thickness of the modifier layer 404 is about 20 nanometers.

The separator 400 prepared in the Example 3 and the bare polypropyleneporous membrane are both heated in the same condition at differenttemperatures for an hour to test their thermal shrinkage resistance. Asthe heat shrinkage rates decrease along the length direction of theseparator 400 and the bare polypropylene porous membrane, the heatshrinkage rates along the width direction of the separator 400 and thebare polypropylene porous membrane are tested. Both the length directionand width direction are coplanar to the surface of the separator 400.Referring to FIG. 8, the separator 400 of the Example 3 has a goodthermal shrinkage resistance at different temperatures compared to theuncoated bare polypropylene porous membrane.

Additionally, electrochemical and safety performances of aLiFePO₄/graphite lithium ion battery having the separator 400 preparedin the Example 3 and a LiFePO₄/graphite lithium ion battery having theuncoated bare polypropylene membrane as the separator therein aretested. The results show that the electrochemical performance of theLiFePO₄/graphite lithium ion battery having the separator 400 does notdecrease, and its thermal stability, and safety performance increases.

(e) Lithium Ion Battery

Referring to FIG. 9, one embodiment of a lithium ion battery 500includes a cathode 502, an anode 504, a separator 506, a non-aqueouselectrolyte solution, and an exterior encapsulating structure 508. Thecathode 502, the anode 504, the separator 506, and the non-aqueouselectrolyte solution are encapsulated by the exterior encapsulatingstructure 508. The separator 506 is disposed between the cathode 502 andthe anode 504. The cathode 502 further includes a cathode currentcollector 512 and a cathode material layer 522 disposed on the surfaceof the cathode current collector 512. The anode 504 further includes ananode current collector 514 and an anode material layer 524 disposed onthe surface of the anode current collector 514. At least one of thecathode current collector 512, the cathode material layer 514, the anodecurrent collector 522, the anode material layer 524, and the separator506 includes the composition of the modifier or the composition of thereaction product of the modifier heated at the heating temperature. Theheating temperature is equal to or higher than 100° C.

The modifier is a mixture of the phosphorus source having the phosphateradical, the trivalent aluminum source, and the metallic oxide in theliquid phase solvent. The composition of the reaction product of themodifier is at least one of Al_(x)M_(y)PO₄ and Al_(x)M_(y)(PO₃)₃. Mrepresents at least one chemical element of Cr, Zn, Mg, Zr, Mo, V, Nb,and Ta. A valence of M is represented by k, wherein 0<x<1, 0<y<1, and3x+ky=3. In one embodiment, the composition of the reaction product isat least one of Al_(x)Cr_(y)PO₄ and

Al_(x)Cr_(y)(PO₃)₃.

The cathode 502 can use the electrode 200 having a cathode materiallayer. Similarly, the anode 504 can use the electrode 200 having ananode material layer. The cathode current collector 512 can use themodified current collector 100 or the current collector 202. The anodecurrent collector 514 can also use the modified current collector 100 orthe current collector 202 of the lithium ion battery.

More specifically, the cathode material layer 522 includes uniformlymixed cathode active material, conductive agent, and binder. The anodematerial layer 524 includes the uniformly mixed anode active material,conductive agent, and binder. The cathode active material in the cathodematerial layer 522 can use the electrode composite material 300 havingthe cathode active material particle or the uncoated cathode activematerial particle 302. Similarly, the anode active material in the anodematerial layer 524 can use the electrode composite material 300 havingthe anode active material particle or the uncoated anode active materialparticle 302.

The lithium ion battery 500 can use the porous membrane 402 or theseparator 400 of the lithium ion battery as the separator 506.

The non-aqueous electrolyte solution includes an electrolyte saltdissolved in an organic solvent. The electrolyte salt can be lithiumhexafluorophosphate (LiPF₆), lithium tetrafluoroborate (LiBF₄), orlithium bis (oxalato) borate (LiBOB). The organic solvent can be atleast one of ethylene carbonate (EC), propylene carbonate (PC),ethylmethyl carbonate (EMC), diethyl carbonate (DEC), and dimethylcarbonate (DMC). The exterior encapsulating structure 508 can be a hardbattery case or a soft encapsulating bag. The lithium ion battery 500can further include a connecting component (not labeled in FIG. 9)achieving an electrical connection between the current collector of thelithium ion battery and the external circuit.

Applying the modifier to the lithium ion battery 500 can improve safetywithout decreasing the electrochemical performance of the lithium ionbattery 500. It can be understood that the modifier is not limited to beapplied to the current collector, electrode active material, andseparator.

Depending on the embodiment, certain steps of methods described may beremoved, others may be added, and the sequence of steps may be altered.It is also to be understood that the description and the claims drawn toa method may include some indication in reference to certain steps.However, the indication used is only to be viewed for identificationpurposes and not as a suggestion as to an order for the steps.

Finally, it is to be understood that the above-described embodiments areintended to illustrate rather than limit the present disclosure.Variations may be made to the embodiments without departing from thespirit of the present disclosure as claimed. Elements associated withany of the above embodiments are envisioned to be associated with anyother embodiments. The above-described embodiments illustrate the scopeof the present disclosure but do not restrict the scope of the presentdisclosure.

1. An electrode of a lithium ion battery, comprising: a currentcollector; an electrode material layer disposed on a top surface of thecurrent collector; and a protective film located on a top surface of theelectrode material layer; wherein a composition of the protective filmis a material selected from the group consisting of Al_(x)M_(y)PO₄,Al_(x)M_(y)(PO₃)₃, and a combination thereof, M represents at least onechemical element selected from the group consisting of Cr, Zn, Mg, Zr,Mo, V, Nb, and Ta, and a valence of M is represented by k, wherein0<x<1, 0<y<1, and 3x+ky=3.
 2. The electrode of claim 1, wherein thecomposition of the protective film is selected from the group consistingof Al_(x)Cr_(1−x)PO₄Al_(x)Cr_(1−x)(PO₃)₃, and a combination thereof. 3.The electrode of claim 1, wherein the electrode material layer comprisesan electrode active material, a conductive agent, and a binder.
 4. Theelectrode of claim 3, wherein the electrode active material comprises acathode active material for a cathode electrode or an anode activematerial for an anode electrode.
 5. The electrode of claim 4, whereinthe cathode active material comprises doped or undoped spinel lithiummanganese oxide, layered lithium manganese oxide, lithium nickel oxide,lithium cobalt oxide, lithium iron phosphate, lithium nickel manganeseoxide, lithium nickel cobalt oxide, or any combination thereof.
 6. Theelectrode of claim 4, wherein the anode active material comprises amaterial selected from the group consisting of lithium titanate,graphite, acetylene black, organic cracking carbon, mesocarbonmicrobeads, and combinations thereof.
 7. The electrode of claim 1,wherein a thickness of the protective film is in a range from about 10nanometers to about 200 nanometers.
 8. The electrode of claim 1, whereina molar ratio of an aluminum element, an M element, and a phosphorouselement in the Al_(x)M_(y)PO₄ or Al_(x)M_(y)(PO₃)₃ is set by(Mol_(Al)+Mol_(Metal)):Mol_(p)—about 1:2.5 to about 1:4, Mol_(Al) is theamount of substance of the aluminum element, Mol_(Metal) is the amountof substance of the M element, and Mol_(p) is the amount of substance ofthe phosphorous element.
 9. The electrode of claim 1, wherein the molarratio is in a range from about 1:2.5 to about 1:3.
 10. A lithium ionbattery, comprising: a cathode; an anode; a separator disposed betweenthe cathode and the anode; a non-aqueous electrolyte solution; and anexterior encapsulating structure encapsulating the cathode, the anode,the separator, and the non-aqueous electrolyte solution in the exteriorencapsulating structure; wherein at least one of the cathode and theanode comprises a current collector, an electrode material layerdisposed on a top surface of the current collector, and a protectivefilm located on a top surface of the electrode material layer; acomposition of the protective film is selected from the group consistingof Al_(x)M_(y)PO₄ and Al_(x)M_(y)(PO₃)₃, M represents at least onechemical element selected from the group consisting of Cr, Zn, Mg, Zr,Mo, V, Nb, and Ta, and a valence of M is represented by k, wherein0<x<1, 0<y<1, and 3x+ky=3.
 11. The lithium ion battery of claim 10,wherein a molar ratio of an aluminum element, an M element, and aphosphorous element in the Al_(x)M_(y)PO₄ or Al_(x)M_(y)(PO₃)₃ is set by(Mol_(Al)+Mol_(Metal)):Mol_(p)=about 1:2.5 to about 1:4, Mol_(Al) is theamount of substance of the aluminum element, Mol_(Metal) is the amountof substance of the M element, and Mol_(p) is the amount of substance ofthe phosphorous element.